Heat exchanger for producing granular salt products



Dec. l5, 1953 E. w. DOUGLASS ETAL 2,662,742

' HEAT EXCHANGER FOR PRODUCING GRANULAR SALT PRODUCTS 5 Sheets-Sheet l Filed Dec. 20, 1948 Dec. l5, 1953 E. w. DouGLAss ErAL 2,662,742`

HEAT EXCHANGER FOR PRODUCTNG GRANULAR SALT PRODUCTS Filed Deo. 20, 1948 3 Sheets-Sheet 2 FlG.-3

FlG.-4

JNVENTOR: Emory W. Douglass 8:

ParkerI S. Dunn ATTORNEY Dec. l5, 1953 E. w. DoUGLAss ETAL 2,662,742

HEAT EXCHANGER FOR PRODUCING GRANULAR SALT PRODUCTS Filed Dec. 20. 1948 3 Sheets-Sheet 5 Emory W. Douglass 8 By Parker S. Dunn ATTORNEY Patented Dec. 15, 1953 HEAT EXCHANGER FOR PRODUCING GRANULAR SALT PRODUCTS Emory W. Douglass and Parker S. Dunn, Carlsbad, N. Mex., assignors to Potash Company of America, Denver, Colo., a corporation of Colorado Application December 20, 1948, Serial No. 66,388 V size. Reference is made to our copending application Serial No, 607,172, led'July 26, 1945, now abandoned, which described but does not claim similar apparatus.

ur invention is particularly adapted for use in treating potash salts such as those obtained from underground deposits mined near Carlsbad, New Mexico, but it should be understood that the apparatus herein disclosed is also adaptable for use in connection with other salts of similar nature.

Fine particles of potassium chloride and similar Ysalts are particularly objectionable not only because of the dust hazard, but also because they exhibit a markedly greater hygroscopicity than coarser particles of the same material, this being generally true of other similar salts. When such salts are exposed for any extended period of time to a relatively moist atmosphere they tend to cake, which increases the difl'iculty encountered in handling and in some instances reduces the utility of the product by reducing its rate of solution or reaction.

A primary object of our invention is to provide apparatus for economically converting fusible salts, particularly potash salts containing a substantial percentage of nes, into granular Crystallite particles having a minimum percentage of fines, and having a relatively low hygroscopicity.

Other objects of major importance include the provision of an improved salt-fusing furnace adapted to partially refine thesalt molten therein; the provision of' fnovel salt-cooling' means adapted to continuously cool' molten salt discharged from our furnace at a rate s'uciently rapid to substantially preventv the formation of crystals or the segregation of saltlcomponents; the provision of salt-cooling means which discharges the solidified salt as relatively coarse flakes having one predetermined dimension; the provision of an improved cooler conveyor discharging the flaked product into a Crusher and the provision of apparatus for establishing a complete cycle of treatment for undersized material or nes.

These aswell as many additional objects and important advantages Yof my apparatus will be clearly understood from the following detailed description and Yfrom which:

the appended drawings in' Y 1 Claim. (Cl. 257-116) Fig. 1 is a diagrammatic view showing the flow of material through our apparatus;

Fig. 2 is a partially sectioned elevation of our cooling device;

Fig. 3 is a plan view of our'cooling device illustrating the relationship of our device tol the furnace;

Fig. 4 is an elevation of our cooling device;

Fig. 5 is a partially sectioned elevation of our furnace; and f Fig. 6 is a partially sectioned elevation of our cooler conveyor.

Our apparatus in brief includes a furnace having a trough-shaped floor sloping towards a discharge spout which is disposed somewhat above floor level and above a cleaning spout through which impurities may be periodically eliminated. The rened salts, asfor` example the salts received from froth flotation treatment, are discharged through suitable openings in the roof of the furnace to form spaced conical piles along the sides of the trough-shaped furnace bottom. As the material on the surface of the cones melts it forms a pool which eventually reaches a sufficient depth to flow from the discharge spout on to a hollow rotating table which is cooled by water circulated internally through the table. This rotating table cools the molten salt very rapidly, the speed of cooling being suicient to substantially prevent the formation of crytals in the material. The solidified salt is removed from the table by a conveyor disposed extending partially across the surface of the table and hav@ ing a series of transverse table-engaging flights which rake the fused salt from the table surface. The initially crushed salts fall into a spiral conveyor through which Aa current of cool air is passed to reduce thev temperature of the material to a point where itmay be readily crushed. Since the air passing through this conveyor picks up considerable dust, it is passed through a suitable separator and the precipitated particles recycled throughlthe furnace. T he conveyor discharges into a suitable crusher which delivers ground salts to screens',"where the vcoarse particles are recycled to the grinder, the fine particles recycled to the furnace, and the particles of the/desired size ranges segregated for packaging. Thus it `may be seen that none of the ne product is wasted and that the type of product produced is by its knature much less hygroscopic thanthe salt in its natural form.k It has also benfound-.that the mechanical strength of the particles, i. e. their resistance to crushing is substantially increased,

thus permitting more severe"y handling ofthe product Without damage. Since all of the apparatus is adapted for continuous operation, very little labor is required in the processing of the material.

Furnace Referdngto Figs: 1". and 5, we? provide amelting furnace having bed I Il and refractory upright side walls II supporting a curved roof I2. With-- in the furnace, generally designated I4, is a trough-shaped oor I3 which slopes-towards the discharge end of the furnace. 'Ihe'roof- I2fis= provided with a series of openings.lrcox'nmunieh cating with hoppers I1 throughywhichisaits; as for example sylvinite ore from aiforthiiiotation treatment, may be fed. The openings I6 are above the portion of the floor I3 lyingeadiacent the side walls I I, and are spaced'a distance suiiicient to permit the salts to form a series of-conit cal piles indicated at |81', Preferably the spacing is-lsueh that;the:peripherie#ofv these.v pilesf` are only slightly'overlapping; thus avoidingqtheffor.- mationi of. a; relatively: continuons ridge*- oft salt along the boundaries of the furnacefiloor I3.l

Ther furnace. I4A iss also provided.' with; an* end wall- I9 havingan exhaustopening 2|- forrgases communicating with a stack 22. From the-:end wallf I9` the' furnaceiloor:V I37 slopes downwardly tclvardsthe.:dischargeI end rwall. 23- of theffurnace which is provided with a lower spout 24-andya discharge-spout 2.6, ,as well.- as: aminspeetion 4door 21. The lower spout 24 slopes inthe-same-direction asfthe7 floor. |3,. but-'isf ata somewhat-.more abrupt angle and :is adapted rtotap .the-lower por:- tion=of a pool.v28 of; meltensalnwhich-forms near the-wall 23; Normally thevspouti24 is` plugged amd vislopenedfr only Zinfrequently to r discharge vimpurities which collect in-theflower portion-of` the pooliz. The dischargefspout 2li-is normally dis.- po'sed: above'- the lowen dischargef spoutz 24 a-nd determines the: depth of. the: pool, Ztl; InV opera'.- tion, the spout 2% isf normally` apen and dischargesV into a, trough 29which delivers molten saltto a. cooling table; generally designated 3|. The furnace I4-may be redzby; gas1 oil; Apowdered coal.. or. the. like,; gas being preferredfor. convenience of operation; and.f cleanliness..

Burners- 321'are preferably disposed inthe end wallf23 and are adapted-.tovdeliverablast. of hot gaa across the-piles I.8-fofisa-lt,.the combustion products being-eventually discharged-through the opening 2|. into;the.stacle.22.. As the salt' on the surface of i the piles. I8. melts;v it iiowsev down the sloping: iloor I3 of theH furnace I4 to, formv the mi.

Cooling table` cooling., table 3|. is, illustrated in. Figs.. 2, 3;. and 4, and includes atabl'e 33. of substantial diameter mounted for rotation, as. on a shaftV 34. Although several diierentmethods. for mountingand drivingthe table.33.. may be adopted'we prefer. to provider the. vertioal shaft. 34 Withv a. collar. 36. uponv which. a. thrust'. bearing. may be mounted. The table 3'3 is hollowv and. includes angupper plate 31 and a lower plate 38- i'oined together by a peripheral wall 3.51 The upper plate 3T may in most instances be iat,A but if desired may be dished very slightly towards the center of rotation to 'assist in preventing accidental spillingM of" the molten salt discharged from the trough 29; The'v elevation of; the edges of the plate-31- should, however; in` this modication not exceed" two` inches with respect to the centerv of the table when the diameter oflv the; table. 1S" ap'- proximatelyftwentyfour feet;A

The upper plate 31 is joined to a cylindrical upright ange 4|, While the lower plate 38 is joined to an inner cylindrical upright flange 42 disposed within and concentric with the flange 4|. A plurality of radially extending pipes 43 are secured to the inner fiange 42,` and extend outwardly between.. the upper;A and: lower plates 31 and 38 to a point near the peripheral wall 39. Cooling water may therefore be fed by a pipe 45 into.a.we1l 44 dened by the inner flange 42 and ow outwardly' through the pipes 43 for discharge into the hollow table 33 near its edge. A dischargeepipe 46;-extends upwardly through the lower plate 33T-intona well 41 deiined by the inner flange42`, the-outer flange, and the lower plate 38, the height'of the pipe 46 above the lower platedening; the maximum elevation of cooling water in the discharge well 41. The discharge pipe 46 rotates with the table and discharges cooling water'which may be fed to the system throughpipe.4i2into3a1circular-trough 43 disposedbelorvrthe. emdzof the? discharge vpipe f 46 :em-diwhichzcommunicateswith;a1sewer` or other suitableA disposalmeanrs..

circular' flange`4 43 isr secured;v to= the under sideof' theel'ower. plate; 38A andis; grooved around itsfperiphery.V to*l receiver thebelt- 5 I engaging the output pulley of a variable speed-speed reducer 53', whichi'may. intturnibef driven' byy asuitable motor: 54:A Aplatesmaybe disposed across the lower: surface of theilangel and supports circularriiangesi 51 tof-whicha circular rail 58 is attaclied:` A hollowV circularibase 53' ismounted on: the floor: andzrotatably'supports a plurality of flanged wheels 6I upon which the rail Sii-rests.

T-hear discharge-spout 2,314 is arranged to deliver molten'. salt. to. table;v 331 at.. a point intermediate the? center.' of: rotation: and circumference, the spout: 29; beingzpreferablyinclined in the directiornofrotationpf; the-,tablesl The-sizev and speed of: rotation off'the: tableA 33 are correlated with thee cooiingfcapacitypf the. table-and the-rate of discharge: of moltenI salt from theY furnace to quicklysolidify; the` molten; saltA as: it; strikes the tailler 3.3? and-f spreads outr into a thinrelatively even. layer: 'Il'1erefore,when =thesalt has traveled through 18o-270 degrees of rotation, it will be solidifledandwilltendxto crackin vertical planes dutathegcontractionnot.the salt upon solidifica.- tion.

To; remove;- the solidified salt from the table 33,. wei provide a scraper, generally designated 32; comprising a frame. 33g extending partially over the table 33 and terminatingat or. near the nm'iphery-'off the, flange.- 4| Sprockets 64, are mounted: ont ashaft; B8; journaled in the frame B31 near its.: extremity.v and;` support. chains, B1 11.0 whichy a pluralityI of.v spaced, laterally extending nights; 68 aresecured. By proper disposition ofthe-iframe 53 theffiightsj-SS-iare causedto engage; the: surfaceofthe tabla33 while the,v chains 61 arebeing driven-.byI suitable. means,V thus Ycolit-inuously ilakingftha solidified salt from. the s urfaceof thetabla33 and ydrawing, the granular material.` acrossthe surface of; the .plate 3 3A to a suitable -receptaclef or discharge; hopper 69,. disposed underv the.- scraperv` 83. aminearthe, periphery of the tabley 33;

Coolefconveyor It. should be that; thel granular salt product; discharged from. the table..- 33 into. libe hopper B5 is only slightlyY belowr the5 Solidiice.- tion point of the: mixture and aubstantia1..l5l abQVe room temperature with the result that its. fri- Vder 12.

l'ability is not at a maximum. It is therefore desirable to cool the relatively coarse salt flakes before crushing to the desired size. For this purpose we provide a cooler conveyor, generally designated 1 I, comprising a cylinder 12 having spiral flights 13 mounted within. The cylinder 12 is rotatably supported in an inclined position by bearings 14 and is rotated by a motor 1'6 having a shaft 11 engaging a bevel pinion gear 18 which meshes with a ring gear 19 secured tothe cylin- The conveyor 1I discharges into a hopper 8| disposed above a suitable crusher 82.

To cool the salt passing through the conveyor 1I we provide a blower 83 or other suitable source of.-.draft near the discharge end of the conveyor 1| and preferably communicating with the interior of the conveyor 1| through an opening 84 having a plurality of downwardly sloping baiiies 86 disposed above the hopper 8|. The hopper 69 is provided with a defiector 81 extending downwardly into the hopper 69 near the charging end of the conveyor 1I, the function of the delflector 81 being to divert a major portion of the air passing through the conveyor 1I into a vent pipe 88, which communicates with a suitable cyclone or similar separator 89. Solid particles separated from the air in the separator 89 are recycled to the hoppers I1 for remelting. Thus it may be seen that the dust or lines generated in the conveyor 1I or in the crusher v82 will be conveyed to the separator 89 and remelted for further processing.

Crusher and screens The crusher 82 may be of any type suitable for operation on material such as salt, as for example an impact Crusher and discharges from a spout 9| on to screens 92, where the ground product is divided into undersize material, standard size material, granular material, and over size. The over size material passes over the screens 92 into a trough 93, where it is elevated by suitable bucket conveyor 94 and discharged through a spout 96 into the hopper 8| for regrinding. The granular materialy which may, for example, be of a size passing through a six mesh screen, but retained on a twenty mesh screen, is discharged into a hopper 91 communieating with a conveyor 98. The standard size material, which may for example pass through a twenty mesh screen but may be retained on a sixty-five mesh screen discharges into a hopper 99 communicating with a conveyor I 0I Material smaller than the desired minimum size may be discharged into a hopper |02 and conveyed by suitable means through a pipe I 03 to either the separator 89 or the hoppers I1 on the furnace I4 for remelting,

Operation It is customary today to refine the relatively impure salts by froth flotation in known manner, which usually requires reduction of the salt to a relatively small particle size. The purified and treated salt from the froth flotation process or such portion of it as is desired is delivered to the hoppers I1 on the furnace |4 and there mixed with the undersized material or nes delivered to the hoppers |1 through the pipe |93, or from the separator 89. either continuously or intermittently fed to the furnace from the hoppers I1 through the openings I to form the conical piles I8 near the walls of the furnace. The heat reflected by the walls of the furnace plus the direct heat The ne material may be yfrom the burners 32A melts the salt on the surface .of the piles I8, which flows along the sloping trough-shaped floor .I3 .of the furnace to form a pool 28. Since the material to be melted is disposed in a series of conical piles rather than in the form of a continuous ridge, a greater surface area is exposed to the heat and the molten material is continuously delivered to the pool 28, thereby preventing insulation of the unmolten material at the base of the cones. The pool 2.8 is quiescent and permitsa settling of various particles having a high specific gravity. These impurities collect in the bottom of the pool near the lower spout 24 and may be periodically discharged. Preferably the amount of heat delivered to the furnace is sufficient to maintain the molten material in the pool 28 at a point only slightly above its solidification point. In' the case of potash salts this is particularly desirable since the molten material is very mobile in nature and tends to flow very easily.

The molten salt is preferably continuously discharged from the furnace I4 to the table 33 in such manner as to spread the molten salt in relatively even layer across the working surface of the table 33, the thickness of the layer of salt preferably being on the order of about an eighth of an inch. The temperature and quantity of the cooling water introduced through the pipe 45 and circulated through hollow table is correlated with the speed of rotation of the table 33 and is suflicient to very rapidly drop the temperature of the molten salt mixture to a point below its solidiflcation or freezing point, thus substantially preventing the formation of crystals and the segregation of components in the salt. In the case of a potassium chloride salt containing -98% KCl we prefer to maintain as closely as possible a discharge temperature at the spout 29 of 755 C. The cooling capacity of the table 33 must therefore be sufficient to reduce this temperature approximately five degrees centigrade in a short period of time, since at the latter temperature the salt will be in a solid condition.

As the salt cools on the table 33 it contracts and shatters into relatively large flakes defined by relatively vertical and irregular planes of fracture extending through the material to the surface of the table 33. These flakes are easily removed by the scraper 82 and delivered through the hopper 69 to the cooler conveyor 1 I. Although the salt flakes are at this point solid, the temperature is still relatively high, which renders the flakes somewhat less friable than is desirable for grinding or crushing. The air passed through the conveyor 1I by the blower 83 reduces the temperature of the salt flakes to a satisfactory point and eliminates a substantial percentage of the fines which would otherwise be delivered to the crusher. It will be understood that since the discharge of the conveyor 1| communicates directly with the hopper 8I1or the grinder 82, all the dust and fines escaping from the grinder 8| will be picked up by the draft sweeping through conveyor 1| and delivered by the vent 88 to the separator 89 for reprocessing.

The crusher 82 is operated at a rate somewhat in excess of its capacity to reduce the percentage of fines formed in the operation, the crushed or oversized material being recycled through the conveyor 94 to the crusher` 82 for reprocessing.

It is to be particularly noted that all of the fines formed at any stageof the operation are recycled to the furnace I4 for remelting, thus maar@ ble minimum. .Since 1the solidified salt `is of a kCrystallite nature, i. e., 'having a structure in which crystals are `substantially non-existent, .very few nes Aare formed in handling of the material and the crushed .material exhibits very little tendency to its original powdered state. It may therefore be handled with very little diniculty, particularly when compared with similar material which has been briquetted and recrushed. The major advantage, however, of this form of process is the reduction in the hygroscopicity of the material, which is markedly less than that of vthe `same Vsalt in 4any other known form.

We contemplate that those skilled in the art may wish to modify our apparatus in certain respects to meet operating conditions peculiar to various installations and .We do not therefore specically limit ourselves to the precise details herein disclosed except insofar as defined by the appended claim.

Having thus described the invention what is claimedis:

Apparatus for cooling molten materials, comprising a drum-type structure having a substantially flat upper surface Vand mounted for rotation about a substantially vertical axis, means including a, central well portion on the upper surface of said drum, a .partition in the well dividing the interior into an inner coolant supply chamber and an .outer discharge chamber and a series of radial conduits extending from the supply chamber through the interior of the drum to a point of discharge adjacent the periphery thereof for circulating the coolant between .the innerand outer chambers, means for circulating a heat exchange medium through the interior o! said structure and in contact with 'said nat surface, means for rotating said structure, means including an overhanging feed spout for feeding molten material onto said upper surface at a downward inclination and directed centrally of the drum, and a mobile scraper member disposed at more than 270 degrees from the point of feed introduction for peeling the matter congealed on the flat surface.

EMORYW. DOUGLASS.

PARKER S..DUNN.

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`1,143,625 Heckenblelkner June 22, 1915 1,173,273 Hubbard, Jr. Feb. 29, 1916 V1,300,799 Williams Apr. 15, 1919 1,312,430 Benjamin Aug. 5, 1919 1,780,201 Martin Nov. 4, 1930 2,115,771 Hellmers May 3, 1938 2,118,438 Lawerenc May 24, 1938 2,205,177 Schlegel June 18, 1940 2,297,505 Schmidberger Sept. 29, 1942 2,446,784 Daley Aug. l0, 1948 

